In an oscillating mirror device which is formed by micromachining technology, a mirror section is supported by two hinges which are provided along the same line, for example. An electrode is provided at a position opposing the mirror section. Due to an electrostatic attraction occurring between the mirror section and the electrode, the mirror section undergoes reciprocating oscillation, with the two hinges acting as twist pivot axes.
As compared to a mirror device in which a polygon mirror is rotated by a motor, such an oscillating mirror device has a simple structure and permits batch processing in a semiconductor process, and thus is easy to be downsized and has a low production cost. Moreover, an oscillating mirror device has a single reflection surface, and therefore suffers no fluctuations in accuracy like those of a polygon mirror having a plurality of faces. Moreover, the operation of an oscillating mirror device is a reciprocating oscillation, which can be made rapid.
Patent Document 1 discloses a mono-axial pivoting type mirror device, and Non-patent Document 1 discloses a bi-axial pivoting type mirror device.
A movable section of a mono-axial pivoting type mirror device is a mirror section that is supported by hinges. The mirror section is isolated from a stationary section by isolation trenches, and the mirror section is driven by an electrostatic attraction which occurs when a driving voltage is applied to the mirror section.
In a bi-axial pivoting type mirror device, an intermediate frame supports a mirror section via hinges, and a stationary section supports the intermediate frame via further hinges, such that the mirror section and the intermediate frame portion constitute a movable section.
With reference to FIG. 10, a bi-axial pivoting type mirror device will be described. FIG. 10 is a perspective view showing a bi-axial pivoting type resonant mirror device 51.
The resonant mirror device 51 includes a first movable section 55 having a mirror face, a second movable section 56 supporting the first movable section 55, and a stationary section 63 supporting the second movable section 56.
The resonant mirror device 51 further includes X hinges 57 and Y hinges 58. The second movable section 56 links to and supports the first movable section 55 via the Y hinges 58. The first movable section 55 is capable of pivoting relative to the second movable section 56 around the Y hinges 58, where the pivot axis is an axis which passes through the Y hinges 58 extending along the Y direction in FIG. 10. The stationary section 63 links to and supports the second movable section 56 via the X hinges 57. The second movable section 56 is capable of pivoting relative to the stationary section 63 around the X hinges 57, where the pivot axis is an axis which passes through the X hinges 57 extending along the X direction in FIG. 10.
At its outer periphery, the first movable section 55 includes X electrode combteeth 59a which generate a driving force for causing a relative displacement of the first movable section 55 with respect to the second movable section 56. At its outer periphery, the second movable section 56 includes Y electrode combteeth 61a which generate a driving force for causing a relative displacement of the second movable section 56 with respect to the stationary section 63.
Moreover, at the inner periphery of the second movable section 56, X electrode combteeth 59b are formed which oppose the X electrode combteeth 59a so as to mesh therewith via a gap. At the inner periphery of the stationary section 63, Y electrode combteeth 61b are formed which oppose the Y electrode combteeth 61a so as to mesh therewith via a gap.
As described above, the first movable section 55 is supported so as to be capable of pivoting relative to the second movable section 56 around the Y hinges 58, and the second movable section 56 is supported so as to be capable of pivoting relative to the stationary section 63 around the X hinges 57, thus realizing the bi-axial pivoting type resonant mirror device 51.
The second movable section 56 includes a first conductive portion 56a for applying a voltage to the first movable section 55, and a second conductive portion 56b to which a different voltage is applied. Because of isolation trenches 64 which are formed between the first conductive portion 56a and the second conductive portion 56b, the first conductive portion 56a and the second conductive portion 56b are split, and are electrically insulated from each other. This makes it possible to independently apply a driving voltage to each of the first movable section 55 and the second movable section 56.
FIG. 11 is a diagram showing a cross section of the resonant mirror device 51. This cross-sectional view corresponds to a D-D cross section in FIG. 10. Referring to FIG. 11, polysilicon is embedded after depositing an insulating layer in the isolation trenches 64, whereby the first conductive portion 56a and the second conductive portion 56b are bonded together in such a manner that the first conductive portion 56a and the second conductive portion 56b will not come apart. As a result, the first conductive portion 56a and the second conductive portion 56b will integrally make a displacement as the second movable section 56.
FIG. 12 is a plan view showing an electrical isolation scheme in the resonant mirror device 51. A voltage Vx applied to an X pad 70 serves as a voltage of the first movable section 55. Assuming that the ground pad 72 is at the ground level (GND), a potential difference of Vx occurs between the first movable section 55 and the second movable section 56.
On the other hand, a voltage Vy which is applied to a Y pad 71 serves as a voltage of the stationary section 63, such that a potential difference of Vy occurs between the stationary section 63 and the second movable section 56.
When Vx and Vy are appropriately controlled, the first movable section 55 and the second movable section 56 will undergo resonation operations at their respective resonant frequencies. As a result, in the bi-axial pivoting type resonant mirror device 51, the pivoting around the X axis and the pivoting around the Y axis of the first movable section 55 can be independently driven under control.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 2004-239987
[Non-patent Document 1] “AN ELECTROSTATICALLY EXCITED 2D-MICRO-SCANNING-MIRROR WITH AN IN-PLANE CONFIGURATION OF THE DRIVING ELECTRODES” (MEMS2000.Proceedings Piscataway, N.J.: IEEE, 2000)